Questions 30-39
The atmosphere of Venus is quite different from ours. Measurements taken from the
Earth show a high concentration of carton dioxide in the atmosphere of Venus. In fact,
carbon dioxide makes up 96 percent of Venus* atmosphere; nitrogen makes up almost all
Line the rest. The Earth's atmosphere, by comparison, is mainly nitrogen, with a fair amount
5 of oxygen as well. Carbon dioxide makes up less than 0.1 percent of the terrestrial atmosphere,
The surface pressure of Venus* atmosphere is 90 limes higher than the pressure of
Earth's atmosphere, as a result of the large amount of carbon dioxide in the former.
Throughout Earth's history, carbon dioxide on Earth has mixed with rain to dissolve
10 rocks; the dissolved rock and carbon dioxide eventually flow into the oceans, where they precipitate to fonn new terrestrial rocks, often with the help of life-forms. If this carbon
dioside were released from the Earth's rocks, along with ower carton dioxide trapped in
seawater, our atmosphere would become as dense and have as high a preasore as that of
Venus. Venus, slightly closer to the Sun than Earth and thus hotter, had no'oceans in
15 which the carbon dioxide could dissolve or life to help take up the carbon.
Also, Venus has probably lost almost all the water it ever had. Since Venus is closer
to the Sun than the Earth is, its lower atmosphere was hotter even early on. The result
was that more water vapor went into its upper atmosphere, where solar ultraviolet rays
broke in up into hydrogen and oxygen. The hydrogen, a light gas, escaped easily; the
20 oxygen has combined with other gasses or with iron on Venus1 surface.
Studies from the Earth show that the clouds on Venus are primarily composed of droplets of sulfuric acid, with water droplets mixed in* Sulfuric acid may sound strange
as a cloud constituent, but the Earth too has a significant layer of sulfuric acid droplets
in its stratosphere. However, the water in the lower layers of the Earth's atmosphere,
25 circulating because of weather, washes the sulfur compounds out of these layers, whereas Venus has sulfur compounds in me lower layers of its atmosphere in addition to those in
its clouds.
【題組】39. The word "constituent” in line 23 is closest in meaning to
(A) type
(B) alternative
(C) product
(D) component
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